Extract from "Webley Air Pistols - Their History and Development" by Gordon Bruce (2001)
"The Tempest model represented the 'last of the series' and was probably the most charasmatic of all Webley air pistols. Built to th every highest standards of the period, it had been thoughtfully designed, well engineered and was of robust appearance. Its imposing dimensions gave the aura of which it certainly matched in performance.
Official factory figures given for pellet speeds acheived by the Tempest model were 420 fps (.177) and 330 fps (.22) but, with proper lubrication and adjustment, velocities reading 530 fps (.177) and 410 fps (.22) could be obtained. Indeed, those pistols aquired in the United States were equipped with more powerfull springs in order to generate such high speeds"